Corn and soybeans grow better together
As the world’s rising population faces increasing challenges of land scarcity, soil degradation, and air pollution from ammonia-based fertilisers, there is an urgent need to identify more sustainable and viable farming practices.
Earth system scientist Dr Amos Tai (Croucher Fellowship 2012), of the Chinese University of Hong Kong, teamed up with life scientists to explore the use of intercropping as a farming technique to replace traditional monocultural practices associated with soil and ammonia-derived acidic air pollution and smog.
Intercropping refers to the growing of two or more crop types in one field. However, this farming practice requires multiple sowing and harvesting, and involves more labour, which has resulted in low adoption in rural communities in China, for example, where urbanisation draws many people from the countryside to work in industry.
The scientists used the advanced DeNitrification-DeComposition (DNDC) computer simulation model to find that intercropping would increase productivity and require less synthetic fertilisers, which in turn would reduce air pollutants emitted from excessive use of such fertilisers. The findings have been published in Environmental Research Letters.
The team compared the intercropping and monoculture of maize and soybean for their crop yields, amount of fertiliser use, and ammonia emitted. Simulations were conducted under the same meteorological conditions, soil properties and farming practices as the testing conditions of a field experiment conducted by a collaborator in Sichuan Agricultural University, China.
Using the computer model, the team predicted what would happen if such a maize (non-legume)-soybean (legume) intercropping system were adopted in all maize and soybean croplands across every Chinese province. The results showed that on land originally designated for maize or soybean production only, intercropping could not only produce the same quantity of maize (4,300-16,000 kg per hectare), but an additional batch of soybean (2,800-5,000 kg per hectare). Moreover, 42 per cent less fertiliser would be required, and 45 per cent less ammonia emitted.
The team fed these results into GEOS-Chem, a 3D atmospheric chemistry model, to compute how such a reduction in ammonia would impact on the formation of fine particulate matters over Chinese provinces. The model predicted that the average annual pollutant concentration could be lowered by up to 1.5 micrograms per cubic metre (2.3 per cent). The resulting improved air quality would be most significant in impact for East and Northeast China provinces.
The study concluded with a cost-benefit analysis of maize-soybean intercropping against the current monocultural farming practice for the two crops. Although additional labour and machinery might double the costs, the nationwide use of intercropping could increase the annual national income by US$67 billion, including US$59 billion from increased crop sales, and US$13 billion saved from air pollution-related public health expenses.
Dr Tai said that the study showed that large-scale adoption of intercropping could benefit the Chinese economy, environment, and people’s health. “We hope this work can help demonstrate the use of a scientific framework to assist policymakers, governments, and other organisations around the globe in evaluating the potential of various sustainable farming methods, and to efficiently allocate their resources to alleviate environmental and food supply issues in the foreseeable future.”
Dr Amos P. K. Tai is an Assistant Professor in the Earth System Science Programme and Graduate Division of Earth and Atmospheric Sciences in the Faculty of Science at the Chinese University of Hong Kong. He received a Croucher Fellowship in 2012 to support postdoctoral research in the Department of Civil and Environmental Engineering at MIT on the impact of climate change and air pollution.
To view Dr Tai’s Croucher profile, please click here.